An ink cartridge plays an important role in the ink jet printer. The ink jet printer can not work without an ink cartridge. The cartridge has an ink-containing medium therein for absorbing the ink. The ink-containing medium is usually a sponge which may be made from many different materials. When the sponge is pressed, a little amount of ink will flow into an ink-containing hole and then be ejected out the ink cartridge through a nozzle. The functions of the sponge within the ink cartridge are absorbing ink and controlling the flowing amount of ink. The sponge in the ink cartridge, undoubtedly, will be in contact with the ink for a long time. The performance of the sponge, however, will get worse and worse after a period of time. For example, dissolution of a portion of the sponge in the ink chokes the nozzle and hinders the printing operation. Another example is that the absorbability of the sponge also gets worse and worse, so it is anticipated to have a trouble of controlling the flowing amount of ink. An excellent ink jet printer should not be accompanied with such problems. There are many kinds of materials for manufacturing sponge in this field because material science has progressed greatly recently. Which kind of sponge is applicable to the ink cartridges of each kind of ink jet printers provided by different manufactures? The sponges made from the same material of different density also makes different performances. In order to be responsible for the performance of the ink jet printer, a simple stability test is needed before applying a new kind of sponge or a novel kind of ink. Moreover, when the manufactures buy a batch of sponges, stability tests of some random samples are necessary steps before adopting this batch of goods.
The conventional method for judging the sponge is to immerse it into ink for a long time and monitor the change of properties of the sponge. The change of properties of the sponge indicates that the properties of the sponge will change in the same manner when it is put into the ink cartridge. The less the change of properties is, the stabler the sponge is. The monitoring tests, however, spend much time because the lifetime of an ink cartridge is not a short period. Providing a simple and short-run method for judging sponge used in the ink cartridge will help the printer manufacturers to select applicable materials for the sponge.